This invention relates to an outboard motor and more particularly to an improved oil reservoir and exhaust system therefore.
As is well known, outboard motors are extremely compact arrangements and as a result of their compact nature and the desire to maintain certain portions relatively small and streamlined, a number of design difficulties are encountered.
For example, although two-cycle engines are widely utilized as the power source in an outboard motor, there is a great deal of interest in the use of four-cycle engines for the power plant in an outboard motor. When a four-cycle engine is employed, the positioning of its oil tank presents certain difficulties. These problems are somewhat magnified by the fact that outboard motors normally position the engine so that its crankshaft rotates about a vertically extending axis. As a result of this orientation, the crankcase chamber cannot form the lubricant reservoir as with other applications for four-cycle engines. Thus it is necessary to provide a separate oil reservoir. The placement of this separate oil reservoir presents certain difficulties. If the oil reservoir is positioned beneath the engine in the power head, then the overall height of the outboard motor becomes excessive. This gives rise to a number of problems not the least of which is the difficulty in tilting up the outboard motor as is typical when not in use. Therefore, it has been proposed to position the oil tank for the engine in the drive shaft housing. There are, however, certain disadvantages with doing so.
One disadvantage is that, again, due to the compact nature of outboard motors, the interior of the drive shaft housing is employed for treating the exhaust gases and silencing them before they are discharged to the atmosphere. Frequently, one or more expansion chambers are formed in the drive shaft housing and the exhaust gas is passed downwardly into the drive shaft housing from the power head through an exhaust pipe that depends into the interior of the drive shaft housing.
Because of this arrangement, the positioning of the oil tank for the engine in the drive shaft housing places it in a location where it is likely to be heated. In fact, in some installations the exhaust pipe actually passes through a cavity around which the oil tank extends and thus a large volume of the oil may be directly exposed to the heat of the exhaust gases.
It has been proposed to attempt to cool the oil tank by draining a portion of the engine cooling water over the exterior surface of the oil tank. Although this may be effective, it has some disadvantages. In the first instance, when the oil tank is cooled by draining water over it, there is difficulty in ensuring adequate and complete cooling. In addition, when operating in marine environments, the evaporation of the water from the heart of the oil tank will leave salt deposits on the oil tank and this can cause corrosion and adversely affect the ability to transfer heat.
It is, therefore, a principal object of this invention to provide an improved oil tank arrangement for an outboard motor.
It is a further object of this invention to provide an improved arrangement for cooling the oil tank of an outboard motor.
It is a still further object of this invention to provide a cooling jacket arrangement for the oil tank of an outboard motor wherein the cooling jacket will be filled with water which is circulated during the entire time when the engine is running.
It is a further object of this invention to provide an improved arrangement for cooling not only the oil tank of an outboard motor but also cooling the exhaust within the drive shaft housing of the motor.
As has been previously noted, the interior of the drive shaft housing is frequently employed to provide one or more expansion chambers for silencing and cooling of the exhaust gases before they are discharged to the atmosphere. However, when the oil tank depends into the drive shaft housing, with the type of arrangements previously proposed, the volume of the drive shaft housing that can be employed as an expansion chamber is substantially reduced.
Therefore, it is a still further principle object of this invention to provide an improved oil tank and expansion chamber arrangement for an outboard motor.
In order to reduce the heating of the lubricant in the oil tank from the exhaust gases, it has ben the practice heretofore to form the expansion chambers for the exhaust treatment at an area below the oil tank. Sometimes, however, the lower surface of the oil tank actually forms the upper surface of the expansion chamber. Such an arrangement obviously not only reduces the volume which can be utilized for the expansion chamber but also can promote excess heat transfer to the lubricant.
It is, therefore, a still further object of this invention to provide an improved arrangement for cooling the oil tank and exhaust system of an outboard motor and wherein a portion of the oil tank can be utilized to define an expansion chamber for exhaust silencing due to the cooling of the oil tank.